U.S. patent number 7,703,284 [Application Number 11/818,003] was granted by the patent office on 2010-04-27 for supercharging system for two-stage supercharging of v-type internal combustion engines.
This patent grant is currently assigned to Robert Bosch GmbH. Invention is credited to Bodo Becker, Oliver Cocca, Guenther Vogt.
United States Patent |
7,703,284 |
Becker , et al. |
April 27, 2010 |
Supercharging system for two-stage supercharging of V-type internal
combustion engines
Abstract
A supercharging system, in particular an at least two-stage
supercharging system, including a first stage and a second stage
for an internal combustion engine having two cylinder banks. The at
least two-stage supercharging system includes at least two charge
air coolers. An exhaust gas turbocharger representing the first
stage and an exhaust gas turbocharger representing the second stage
are each situated next to one of the cylinder banks of the internal
combustion engine.
Inventors: |
Becker; Bodo (Oberlaindern,
DE), Vogt; Guenther (Holzkirchen, DE),
Cocca; Oliver (Munchen, DE) |
Assignee: |
Robert Bosch GmbH (Stuttgart,
DE)
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Family
ID: |
38663817 |
Appl.
No.: |
11/818,003 |
Filed: |
June 12, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080034752 A1 |
Feb 14, 2008 |
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Foreign Application Priority Data
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Jun 12, 2006 [DE] |
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10 2006 027 117 |
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Current U.S.
Class: |
60/612; 60/323;
123/563; 123/562 |
Current CPC
Class: |
F02B
37/18 (20130101); F02B 37/004 (20130101); F01N
13/143 (20130101); F02B 37/013 (20130101); F02B
37/001 (20130101); F02B 29/0418 (20130101); F02B
29/0412 (20130101); F02B 37/002 (20130101); F02B
37/02 (20130101); F02B 37/162 (20190501); Y02T
10/12 (20130101); F02B 75/22 (20130101); F01N
13/107 (20130101); Y02T 10/146 (20130101); Y02T
10/144 (20130101) |
Current International
Class: |
F02B
33/44 (20060101); F01N 1/00 (20060101); F02B
37/00 (20060101); F02B 37/013 (20060101); F02B
37/007 (20060101); F02B 29/04 (20060101); F02B
33/00 (20060101) |
Field of
Search: |
;60/612,323 ;123/562-563
;73/118.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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10060690 |
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Jun 2002 |
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DE |
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0 718 481 |
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Jun 1996 |
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EP |
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Other References
Bosch, Kraftfahrtechnisches Taschenbuch [Automotive Handbook],
23.sup.rd Edition, Vieweg, 1999, pp. 445 and 446. cited by
other.
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Primary Examiner: Trieu; Thai Ba
Attorney, Agent or Firm: Kenyon & Kenyon LLP
Claims
What is claimed is:
1. A supercharging system for an internal combustion engine having
two cylinder banks, comprising: at least two charge air coolers; a
first exhaust gas turbocharger representing a first stage of the
supercharging system; a second exhaust gas turbocharger
representing a second stage of the supercharging system; and a
first nonreturn valve; wherein: each of the first and second
exhaust gas turbochargers is situated next to one of the cylinder
banks of the internal combustion engine; the charge air coolers are
situated in a parallel circuit, and partial flows of fresh air
passing through them are combined at a junction connected upstream
from a throttle device; and the first nonreturn valve is situated
upstream from the junction in a branch downstream from a first of
the charge air coolers.
2. The supercharging system according to claim 1, wherein the
exhaust gas turbochargers each include a compressor part and a
turbine part, and the turbine part of the second exhaust gas
turbocharger is connected to an exhaust gas manifold via a
connecting line.
3. The supercharging system according to claim 2, wherein the
connecting line opens into the exhaust gas manifold downstream from
a regulating device and upstream from the turbine part of the first
exhaust gas turbocharger.
4. The supercharging system according to claim 2, wherein the
exhaust gas turbochargers of the supercharging system are situated
in an area of end faces of the internal combustion engine having
two cylinder banks.
5. The supercharging system according to claim 2, wherein the
connecting line and the exhaust gas manifold are designed as air
gap insulated pipes.
6. The supercharging system according to claim 2, wherein, with
respect to a longitudinal axis of a vehicle in which the
supercharging system is included, the two cylinder banks are
serially positioned between the first and second exhaust gas turbo
chargers.
7. The supercharging system according to claim 1, wherein with
respect to a longitudinal axis of a vehicle in which the
supercharging system is included, the charge air coolers are
situated in front of or in back of the cylinder banks.
8. The supercharging system according to claim 1, wherein the
supercharging system is a two-stage supercharging system.
9. The supercharging system according to claim 1, further
comprising a second nonreturn valve parallel-connected to a
compressor part of the second exhaust gas turbocharger.
10. The supercharging system according to claim 9, wherein the
exhaust gas turbochargers each include a compressor part and a
turbine part, and the turbine part of the second exhaust gas
turbocharger is connected to an exhaust gas manifold via a
connecting line.
11. The supercharging system according to claim 10, wherein the
connecting line opens into the exhaust gas manifold downstream from
a regulating device and upstream from the turbine part of the first
exhaust gas turbocharger.
12. The supercharging system according to claim 10, wherein the
exhaust gas turbochargers of the supercharging system are situated
in an area of end faces of the internal combustion engine having
two cylinder banks.
13. The supercharging system according to claim 10, wherein the
connecting line and the exhaust gas manifold are designed as air
gap insulated pipes.
14. The supercharging system according to claim 9, wherein with
respect to a longitudinal axis of a vehicle in which the
supercharging system is included, the charge air coolers are
situated in front of or in back of the cylinder banks.
15. The supercharging system according to claim 9, wherein the
supercharging system is a two-stage supercharging system.
16. A supercharging system for an internal combustion engine having
two cylinder banks, comprising: at least two charge air coolers; a
first exhaust gas turbocharger representing a first stage of the
supercharging system; a second exhaust gas turbocharger
representing a second stage of the supercharging system; and a
nonreturn valve; wherein: each of the first and second exhaust gas
turbochargers is situated next to one of the cylinder banks of the
internal combustion engine; the charge air coolers are situated in
a parallel circuit, and partial flows of fresh air passing through
them are combined at a junction connected upstream from a throttle
device; and the nonreturn valve is parallel-connected to a
compressor part of the second exhaust gas turbocharger.
17. The supercharging system according to claim 16, wherein the
exhaust gas turbochargers each include a compressor part and a
turbine part, and the turbine part of the second exhaust gas
turbocharger is connected to an exhaust gas manifold via a
connecting line.
18. The supercharging system according to claim 17, wherein the
connecting line opens into the exhaust gas manifold downstream from
a regulating device and upstream from the turbine part of the first
exhaust gas turbocharger.
19. The supercharging system according to claim 17, wherein the
exhaust gas turbochargers of the supercharging system are situated
in an area of end faces of the internal combustion engine having
two cylinder banks.
20. The supercharging system according to claim 17, wherein the
connecting line and the exhaust gas manifold are designed as air
gap insulated pipes.
21. The supercharging system according to claim 16, wherein the
supercharging system is a two-stage supercharging system.
Description
BACKGROUND INFORMATION
The power limits of a supercharging system such as an exhaust gas
turbocharger are increased, for example by regulated two-stage
supercharging, as is known from Bosch, Kraftfahrtechnisches
Taschenbuch [Automotive Handbook], 23.sup.rd Edition, Vieweg, 1999,
pages 445 through 446. In regulated two-stage supercharging, two
exhaust gas turbochargers of different sizes are connected in
series. The exhaust gas mass flow first flows into an exhaust gas
manifold. From there, the exhaust gas mass flow is expanded via a
high pressure turbine. In the case of large exhaust gas volumes,
which can occur at high speeds, a portion of the exhaust gas mass
flow may be redirected around the high pressure turbine via a
bypass. The entire exhaust gas mass flow is subsequently used by a
low pressure turbine connected downstream from the high pressure
turbine. The incoming fresh air mass flow is first precompressed by
a low pressure stage and then further compressed in the high
pressure stage. Ideally, the fresh air mass flow undergoes
intermediate cooling between the low pressure stage and the high
pressure stage.
At approximately 50% to 60% of the nominal speed, the exhaust gas
is completely redirected around the high pressure turbine via a
bypass. As a result, the high pressure compressor, which is driven
by the high pressure turbine and is connected in series to a low
pressure compressor driven by the low pressure turbine, is
simultaneously taken out of operation. In this case, the high
pressure compressor is bypassed via a charge air line in which a
nonreturn valve is provided to prevent charge air from flowing back
via the charge air line during operation of the high pressure
compressor.
Two-stage supercharging in a supercharging system is generally
carried out by two series-connected exhaust gas turbochargers. This
achieves a two-stage expansion via the two turbine parts of the two
exhaust gas turbochargers as well as a two-stage compression on the
compressor side of the two series-connected exhaust gas
turbochargers. The disadvantages of unregulated two-stage
supercharging are avoided by regulating devices for bypassing the
high pressure turbine and high pressure compressor.
Cutting off the exhaust gas mass flow upstream from the high
pressure turbine regulates the power of the high pressure turbine.
The exhaust gas mass flow leaving the high pressure turbine mixes
with a portion of the exhaust gas mass flow flowing through the
bypass valve and is subsequently expanded in the low pressure
turbine. A disadvantage of this procedure is the fact that the
difference in pressure present between the outlet side of the
internal combustion engine and the output of the high pressure
turbine is expanded by a bypass valve without reducing work. In the
case of unregulated two-stage supercharging, the fact that the
entire exhaust gas mass flow is expanded in an unregulated manner
in the high pressure and low pressure turbines is disadvantageous.
This means that the power of the two-stage supercharging system
rises in an unregulatable manner between a specific load point and
the maximum load point, which is unsuitable for use in an internal
combustion engine of a passenger car. Due to the design of the high
pressure and low pressure turbines in the case of unregulated
two-stage supercharging, an unsatisfactory response characteristic
exists in the operating range up to and above the design point.
European Patent Application No. EP 0 718 481 relates to an exhaust
gas recirculation system for a supercharged internal combustion
engine. To lower exhaust emissions, in particular to substantially
reduce NO.sub.x levels in the partial load range of the internal
combustion engine, a method is known for recirculating a portion of
the exhaust gas to suppress NO.sub.x formation by reducing the
oxygen content. In supercharged engines, recirculating the exhaust
gas directly results in a noticeable decrease in the power of the
exhaust gas turbine. This decrease is even more pronounced in a
two-stage supercharging system. To avoid power decreases of this
type, which usually go hand-in-hand with increased fuel
consumption, a method is described in which the exhaust gas to be
recirculated is removed from between the high pressure turbine part
and the low pressure turbine part and supplied to the inlet of the
low pressure compressor which is higher in relation to the low
pressure turbine. This ensures an exhaust gas recirculation method
which minimizes increased fuel consumption.
The design of a two-stage supercharging system poses a particular
difficulty in internal combustion engines having a V-shaped
cylinder layout, because the two cylinder banks must be uniformly
impinged upon by the turbochargers. If only one turbocharger is
used as the high pressure stage and one turbocharger as the low
pressure stage, the supercharging system may be positioned in front
of or behind the internal combustion engine without taking up a lot
of space. Although this provides a number of advantages, it
nevertheless has the disadvantage that there is not always enough
room in the engine compartment.
SUMMARY OF THE INVENTION
According to the present invention, the two stages of a two-stage
supercharging system should each be accommodated on the side of an
internal combustion engine, or a flat engine, having a V-shaped
cylinder bank layout mounted in the longitudinal direction in
relation to the vehicle. In the design according to the present
invention, two embodiment variants are provided below, one
embodiment variant representing a supercharging system having
intermediate cooling and the other embodiment variant representing
a supercharging system having no intermediate cooling.
In the two-stage supercharging system having intermediate cooling
according to the present invention, the air compressed by the low
pressure compressor of the two-stage supercharging system is
precooled in a heat exchanger on the fresh air side. The heat
exchanger may be conveniently accommodated in an advantageous
manner in the wheel box located on the same side of the vehicle.
Downstream from this intercooler, the intermediately cooled,
precompressed fresh air may be supplied to a charge air cooler via
both the high pressure compressor and a bypass line. The bypass
line is advantageously released by an automatic compressor
bypass.
The charge air cooler may be accommodated in a particularly
advantageous manner in the area of a wheel box in the engine
compartment. In the case of a two-stage supercharging system having
no intermediate cooling, two charge air coolers are employed which
are used for final cooling of the fresh air precompressed in the
low pressure compressor and in the high pressure compressor before
entering the combustion chambers of the internal combustion engine.
In this embodiment variant, both charge air coolers may be
parallel-connected in a particularly advantageous manner, which
enables the pressure loss to be minimized on the fresh air side.
Bypass valves may be used to cut off the flow through the two
charge air coolers when, for example, the high pressure compressor
is in use, and the pressure may be built up faster thereby due to
smaller container volumes. According to the embodiment variant of
the two-stage supercharging system having no intermediate cooling,
the two exhaust gas turbochargers may also be positioned to the
left and right of the internal combustion engine. The exhaust gas
manifolds of the internal combustion engine are connectable to each
other via a common exhaust gas line.
According to a preferred embodiment of the above-outlined
embodiment variant of the supercharging system according to the
present invention for internal combustion engines having V-shaped
cylinder bank layouts or designed as flat engines, the
supercharging systems are connected to the relevant cylinder bank
as far to the front or rear as possible, i.e., viewed in relation
to the direction of vehicle travel, on an end face of the engine
(in front) or a back end of the engine (in the rear). This results
in short exhaust gas pipes leading to the cylinder banks, and
minimal flow losses as a consequence thereof, as well as an
end-face surface that dissipates little heat. In a preferred
embodiment with regard to the efficiency of the overall system, a
thermally insulated design of the exhaust gas system, in particular
of connecting lines, is provided, using air gap insulated pipes
between the supercharging systems and the cylinder banks. The
design according to the present invention supports the shortest
possible connecting pipes so that the flow losses may be kept
within narrow limits.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic illustration of a two-stage supercharging
system including regulation.
FIG. 2 shows a two-stage supercharging system including
series-connected charge air coolers having intermediate
cooling.
FIG. 3 shows a two-stage supercharging system including
parallel-connected charge air coolers having no intermediate
cooling.
DETAILED DESCRIPTION
The illustration according to FIG. 1 shows a schematic flow chart
of a regulated two-stage supercharging system.
According to the illustration in FIG. 1, a two-stage supercharging
system 12 has a first exhaust gas turbocharger 14 and a second
exhaust gas turbocharger 24. Fresh air 10, which has a state (1),
is compressed via a low pressure compressor part 16 of first
exhaust gas turbocharger 14. The precompressed fresh air is cooled
in a first charge air cooler 22 connected downstream from low
pressure compressor part 16 of first exhaust gas turbocharger 14.
In addition to low pressure compressor part 16, first exhaust gas
turbocharger 14 also includes a low pressure turbine part 20 which
is coupled with low pressure compressor part 16 via a shaft. After
passing through first charge air cooler 22, the precompressed fresh
air flows to a high pressure compressor part 26 of a second exhaust
gas turbocharger 24. High pressure compressor part 26 of second
exhaust gas turbocharger 24 may also be bypassed via a first bypass
32, so that the precompressed fresh air flows directly to a second
charge air cooler 34 in which the precompressed fresh air is
recooled.
If the precompressed fresh air cooled in first charge air cooler 22
is supplied to high pressure compressor part 26 of second exhaust
gas turbocharger 24, the precompressed fresh air which was cooled
in first charge air cooler 22 may be compressed again. In addition
to high pressure compressor part 26, second exhaust gas
turbocharger 24 also includes a high pressure turbine part 28. High
pressure compressor part 26 and high pressure turbine part 28 of
second exhaust gas turbocharger 24 are coupled with each other via
a shaft 30.
A second charge air cooler 34 is connected downstream from first
bypass 32 and high pressure compressor part 26, respectively.
Either the fresh air which was recompressed in high pressure
compressor part 26 of second exhaust gas turbocharger 24 or the
precompressed fresh air passing through first bypass 32 is recooled
in this second charge air cooler. On the inlet side of an internal
combustion engine 36, the fresh air leaving second charge air
cooler 34 assumes state (2). Exhaust gas leaves internal combustion
engine 36 on the outlet side and assumes a state (3), the exhaust
gas being supplied to the exhaust gas tract of internal combustion
engine 36 via an exhaust line 38. The exhaust gas may be routed via
either a second bypass 40 or high pressure turbine part 28 of
second exhaust gas turbocharger 24. At the output of high pressure
turbine part 28, the exhaust gas assumes state (3') before flowing
to either low pressure turbine part 20 or a third bypass 44 via a
supply line 42. After passing through low pressure turbine part 20,
the exhaust gas assumes state (4), the pressure in state (4) being
essentially equal to the ambient pressure.
The illustration according to FIG. 2 shows a two-stage
supercharging system for an internal combustion engine having at
least two cylinder banks and including series-connected charge air
coolers having intermediate cooling.
According to FIG. 2, fresh air 10 flows to an air filter 50,
downstream from which a mass air flow meter 52 is connected. Fresh
air 10 is precompressed in low pressure compressor part 16 of first
exhaust gas turbocharger 14, low pressure compressor part 16 of
first exhaust gas turbocharger 14 being coupled with low pressure
turbine part 20 via shaft 18. The precompressed fresh air is cooled
in first charge air cooler 22. The precompressed, cooled fresh air
subsequently flows to high pressure compressor part 26 of second
exhaust gas turbocharger 24 via a branch 54. High pressure
compressor part 26 of second exhaust gas turbocharger 24 is
connected to high pressure turbine part 28 via shaft 30 and driven
via high pressure turbine part 28 of second exhaust gas
turbocharger 24. The fresh air which was recompressed in high
pressure compressor part 26 of second exhaust gas turbocharger 24
flows to second charge air cooler 34, in which the recompressed
fresh air is cooled again. A valve 56, which is designed, for
example, as a nonreturn valve, is provided between first charge air
cooler 22 and second charge air cooler 34, which are situated in a
series circuit 74, to prevent the fresh air which was recompressed
in high pressure turbine part 26 of second exhaust turbocharger 24
from flowing back in the direction of first charge air cooler 22
before passing through second charge air cooler 34, so that
pressure losses are avoided. The highly compressed fresh air which
was recooled in second charge air cooler 34 flows to internal
combustion engine 36 via a throttle device 58. Internal combustion
engine 36 according to the illustration in FIG. 2 includes a first
cylinder bank 60 and a second cylinder bank 62 according to the
design principle of V-type engines. These are generally internal
combustion engines 36 having 6, 8, 10, 12 or more cylinders which
are used in high-performance passenger cars or commercial vehicles,
including spark-ignition and auto-ignition internal combustion
engines 36. The individual cylinders accommodated in cylinder banks
60 and 62, respectively, are identified by reference numeral 64. An
inlet side on which the highly compressed and cooled fresh air
enters the combustion chambers of cylinders 64 downstream from
throttle device 58 is indicated by reference numeral 66 in the
illustration according to FIG. 2, while reference numeral 68
identifies the outlet side where the exhaust gas leaves the
combustion chambers of internal combustion engine 36. On the outlet
side, internal combustion engine 36 having two cylinder banks 60,
62 includes exhaust gas manifolds which empty into a common exhaust
gas line 38. Common exhaust gas line 38, which runs in the exhaust
gas tract of the internal combustion engine, accommodates an
exhaust gas regulating device 70, and a supply line which is
connected downstream from high pressure turbine part 28 of second
exhaust gas turbocharger 24 empties downstream from this exhaust
gas regulating device. Low pressure turbine part 20 of first
exhaust gas turbocharger 14, in which the exhaust gas is fully
expanded and leaves the exhaust gas tract of the internal
combustion engine in a cleaned and expanded state in the form of
exhaust gas 72, which essentially has the ambient pressure level,
is accommodated downstream from the point at which the supply line
from high pressure turbine part 28 empties into exhaust gas line
38. The supply line from high pressure turbine part 28 of second
exhaust gas turbocharger 24 to exhaust gas line 38 is identified by
reference numeral 76 in the illustration according to FIG. 2.
In the two-stage supercharging system illustrated in FIG. 2, fresh
air 10 flowing through low pressure compressor part 16 is precooled
by first charge air cooler 22. This first charge air cooler may be
conveniently accommodated in a particularly advantageous manner in
front of or behind one of the wheel boxes in the area of the engine
compartment located, for example, next to first cylinder bank 60.
After leaving first charge air cooler 22, the precompressed fresh
air may flow through both high pressure compressor part 26 of
second exhaust gas turbocharger 24 and a bypass line, which is
assigned to high pressure compressor part 26 and accommodates
nonreturn valve 56. The bypass line accommodating nonreturn valve
56, which runs parallel to high pressure compressor part 26 of
second exhaust gas turbocharger 24, may also be provided with an
automatic compressor bypass. Second charge air cooler 34 may be
advantageously accommodated in the area of the vehicle engine
compartment facing second cylinder bank 62 of internal combustion
engine 36. The two-stage supercharging system provided according to
the present invention, including series-connected charge air
coolers 22, 34 having intermediate cooling, may be advantageously
accommodated in the vehicle so that first charge air cooler 22 and
first exhaust gas turbocharger 14 are located adjacent to first
cylinder bank 60 of internal combustion engine 36, while second
exhaust gas turbocharger 24 and second charge air cooler 34 are
situated on the side facing second cylinder bank 62 of internal
combustion engine 36. Since the vehicle wheel boxes are connectable
to the surroundings, accommodating series-connected first and
second charge air coolers 22, 34 in the area of the wheel boxes for
the front wheels in the engine compartment makes it possible to
particularly effectively cool either fresh air 10 which was
precompressed in low pressure compressor part 16 or the
recompressed fresh air entering second charge air cooler 34. If
exhaust gas regulating valve 70 is closed, the entire exhaust gas
mass flow may be first supplied to high pressure turbine part 28 of
second exhaust gas turbocharger 24.
A further connecting line 76 is routed around internal combustion
engine 36 having two cylinder banks 60, 62 to supply the exhaust
gas leaving high pressure turbine part 28 to low pressure turbine
part 20 of first exhaust gas turbocharger 14. Low pressure turbine
part 20 is situated on the side of internal combustion engine 36
where the latter's first cylinder bank 60 is located. An attempt
should be made to keep the pipes, i.e., connecting line 76 from
high pressure turbine part 28 to exhaust gas line 38 as well as the
section of exhaust gas line 38 from outlet side 68 of internal
combustion engine 36 to low pressure turbine part 20, as short as
possible to keep flow losses to a minimum, in particular, to
minimize the heat-dissipating surface of exhaust gas line 38 and
connecting line 76, respectively. The thermally insulated design of
the exhaust gas system, in particular of the connecting lines
between the supercharging systems and the cylinder banks using air
gap insulated pipes, is particularly advantageous for the
embodiment variant of the two-stage supercharging system
illustrated in FIG. 2. In the design according to the present
invention, the connecting lines may be kept very short.
The illustration according to FIG. 3 shows an embodiment variant of
the two-stage supercharging system for internal combustion engines
having two cylinder banks, in which the charge air coolers are
parallel-connected and there is no intermediate cooling of the
fresh air.
According to the embodiment variant illustrated in FIG. 3, fresh
air 10 flows via air filter 50 and mass air flow meter 52 to low
pressure turbine part 16 of first exhaust gas turbocharger 14. As
illustrated in connection with FIG. 2, low pressure compressor part
16 of first exhaust gas turbocharger 14 is connected to low
pressure turbine part 20 of first exhaust gas turbocharger 14 via
shaft 18. On the one hand, precompressed fresh air 10 flows to high
pressure compressor part 26 of second exhaust gas turbocharger 24
via a bypass line 82 and on the other hand passes, in part, through
a branch 80, which runs to first charge air cooler 22. A first
nonreturn valve 84 is connected downstream from first charge air
cooler 22 for cooling precompressed fresh air 10. First nonreturn
valve 84 performs a sequence valve function when the pressure loss
in charge air cooler 34 increases. Fresh air 10 which was
precompressed in low pressure compressor part 16 flows to a
junction 88. The flow of precompressed fresh air passing through
bypass line 82 flows to high pressure compressor part 26 of second
exhaust gas turbocharger 24. A further, second nonreturn valve 86
is parallel-connected thereto. Second nonreturn valve 86 acts as a
compressor bypass when low pressure compressor part 16 supplies an
excessive air volume and high pressure compressor part 26 switches
to "blocked mode."
Fresh air 10 which was recompressed in high pressure compressor
part 26 is cooled in charge air cooler 34 connected downstream from
high pressure compressor part 26 and supplied to junction 88, which
is located upstream from throttle device 58. The highly compressed
fresh air flow leaving second charge air cooler 34 and the portion
of the fresh air flow which was cooled in first charge air cooler
22 via branch 80 mix in junction 88 and flow via first nonreturn
valve 84 of junction 88. The illustration according to FIG. 3 shows
that first charge air cooler 22 and second charge air cooler 34 are
situated in a parallel circuit 90. Throttle device 58, via which
the precompressed fresh air flows on inlet side 66 to cylinders 64
of first cylinder bank 60 and second cylinder bank 62 of internal
combustion engine 36, is located downstream from junction 88 and
upstream from internal combustion engine 36. When exhaust gas
regulating valve 70 is closed, exhaust gas flows from outlet side
68 to high pressure turbine part 28 of second exhaust gas
turbocharger 24 and is resupplied, via connecting line 76, to
exhaust gas line 38 downstream from exhaust gas regulating valve 70
and upstream from low pressure turbine part 20 of first exhaust gas
turbocharger 14. After the exhaust gas has been fully expanded in
low pressure turbine part 20, exhaust gas 72 leaves the exhaust gas
tract of the internal combustion engine at the ambient pressure
level.
In the embodiment variant of the two-stage supercharging system
according to the illustration in FIG. 3, first exhaust gas
turbocharger 14 may be situated on the side of internal combustion
engine 36 where first cylinder bank 60 is located. Likewise, second
exhaust gas turbocharger 24 may be situated diametrically opposed
to second cylinder bank 62 of internal combustion engine 36. An
attempt should be made to keep both connecting line 76 to high
pressure turbine part 28 of second exhaust gas turbocharger 24 to
exhaust gas line 38 as well as exhaust gas line 38 to low pressure
turbine part 20 as short as possible to minimize flow losses on the
one hand and, to minimize the heat-dissipating surfaces of these
pipes, i.e., exhaust gas line 38 and connecting line 76 on the
other hand.
In the two-stage supercharging systems illustrated in FIGS. 2 and
3, providing the exhaust gas lines, i.e., pipes 76 and 38, with a
thermally insulated design and using air gap insulated pipes have
an advantageous effect on the efficiency of the overall system.
In the two embodiment variants according to FIGS. 2 and 3, exhaust
gas turbochargers 14 and 24, respectively, should be situated as
far as possible to the front or rear of cylinder banks 60, 62 of
internal combustion engine 36 having a V-shaped cylinder layout. If
both exhaust gas turbochargers 14 and 24 are located as close as
possible to cylinder banks 60 and 62, respectively, their distance
from one another is minimized and pipes 76 and 38 may be kept as
short as possible. To utilize the compact mounting space in the
engine compartment of a motor vehicle which includes an internal
combustion engine 36 having a V-shaped cylinder layout, connecting
line 76, which connects high pressure turbine part 28 of second
exhaust gas turbocharger 24 to exhaust gas line 38 leading to low
pressure turbine part 20 of first exhaust gas turbocharger 14, is
routed in the engine compartment in such a way that pipes do not
have to be routed beneath the oil pan of internal combustion engine
36.
* * * * *